Can I convert my B1/B2 visa to a work visa while I'm still in the U.S., or do I have to leave and apply from my home country?

Yes, but be careful. While you can apply for a change of status from B1/B2 to a work visa without leaving the U.S., it’s not guaranteed. USCIS scrutinizes these cases closely, especially if they suspect you entered the U.S. with the intent to work

Totally doable,but with a few caveats. You can switch from a B1/B2 to a work visa like H-1B while you're in the U.S., but it depends on your situation and having a job offer from an employer who’s ready to sponsor you

You must not begin employment until your change of status is approved by USCIS. Additionally, you must have a U.S. employer willing to sponsor you, and they must file a petition on your behalf